# -*- coding: utf-8 -*-


__author__ = 'raniys'


# 0, 1, 1, 2, 3, 5, 8, 13
def feibo(n):
    a = 0
    b = 1
    i = 1
    while i < n:
        a, b = b, a + b
        i += 1
    return a


print feibo(5)

